[Dbix-class] patch for ResultSet::find_or_new

Tue Jan 15 08:40:50 GMT 2008

BTW:

http://search.cpan.org/~ash/DBIx-Class-0.08008/lib/DBIx/Class/ResultSet.pm#ATTRIBUTES
doesn't contain the "key" attribute.

Am 15.01.2008 um 08:00 schrieb Zbigniew Lukasiak:

> On Jan 14, 2008 10:59 PM, Jason Kohles <email at jasonkohles.com> wrote:
>>
>> On Jan 14, 2008, at 2:19 PM, Zbigniew Lukasiak wrote:
>>
>>> On Jan 13, 2008 7:20 PM, Matt S Trout <dbix-class at trout.me.uk>  
>>> wrote:
>>>> On Sun, Jan 13, 2008 at 10:41:43AM +0100, Patrick Weemeeuw wrote:
>>>>> There is a small bug in find_or_new: when the find part
>>>>> fails, it calls new_result with the hash containing the
>>>>> values that were used for the search. It should use no
>>>>> values at all instead.
>>>>
>>>> This isn't a bug. If that's the behaviour you want, do
>>>>
>>>> my $o = $rs->find({ id => $id }) || $rs->new({});
>>>>
>>>>> Example buggy case: $o = $...->find_or_new( { id => $id } )
>>>>> with id a not null primary key. When $id is undefined, there
>>>>> is obviously no row in the DB, and a new result object is
>>>>> returned. However, the object returned contains the column
>>>>> id => NULL, which (1) is invalid for this kind of object,
>>>>> and (2) prevents in some backends (e.g. Pg) that the
>>>>> sequence is used to generate a unique id.
>>>>
>>>> So don't pass id if it isn't a valid value. Passing undef there is
>>>> a bug
>>>> in your code, not in DBIx::Class.
>>>>
>>>> The usual use of find_or_new is to pass a unique key plus  
>>>> additional
>>>> attributes to be used for object creation (which are ignored in the
>>>> find()
>>>> by specifying the key attr as well). Consider for example
>>>>
>>>> my $stats = $schema->resultset('PageViews')->find_or_new(
>>>>             { page => $page, views => 0 },
>>>>             { key => 'page' }
>>>>           );
>>>>
>>>
>>> How can we excercise the _or_new part of find_or_new?
>>>
>>
>> The results you are seeing are *exactly* the way it is expected to
>> work.  In this example you are doing:
>>
>> $rs->find_or_new( { id => undef } )
>>
>> and getting back an object where id is undefined.  How is that
>> mysterious or incorrect behaviour?  You told it 'find me a row in the
>> database where id is undef, and if you can't find one, create a new
>> object where id is undef' and that's exactly what it did.
>>
>> The big difference between ->find_or_new and ->find_or_create, is  
>> that
>> ->find_or_new doesn't attempt to do the insert yet, and so is not
>> guaranteed to return to you an object that even *can* be inserted.
>> What I would do in this case is either not use ->find_or_new when you
>> don't have a valid primary key, or do something like this:
>>
>> my $obj = $rs->find_or_new( $id ? { id => $id } : {} );
>>
>> or even...
>>
>> my $obj = $rs->find_or_new( { id => $id } );
>> if ( ! defined $obj->id ) { $obj->id( 'foo' ) }
>>
>>
>>>> From the above I conclude that we should omit 'page' in the request
>>> (instead of setting it to 'undef'):
>>>
>>
>>> my $stats = $schema->resultset('PageViews')->find_or_new(
>>>              { views => 0 },
>>>              { key => 'page' }
>>>            );
>>> but then if we have another record with views == 0 it will be found
>>> and no new row would be created.
>>>
>> You've just created an even more bizarre situation, what you have now
>> is essentially
>>
>> my $rs = $schema->resultset( 'PageViews' );
>> my $stats = $rs->find( {} ) || $rs->new( { views => 0 } );
>>
>>
>> The documentation for find_or_create says "Tries to find a record
>> based on its primary key or unique constraint; if none is found,
>> creates one and returns that instead."  What you are trying to do is
>> use it without providing a primary key or a unique constraint, and  
>> the
>> behavior you are seeing is exactly what I would expect to happen in
>> that situation, since ->find can't match anything without a primary
>> key or a unique constraint, you get back a new object instead.
>
> No - that is not what would happen.  No new record will be created if
> you have another record that have views == 0.
> This is very important - the behaviour is not what is documented - but
> it is intentional - as the comment in the code shows.
>
> --
> Zbigniew
>
>
>>> This is because find falls back on finding by all columns in the  
>>> query
>>> (ie by 'views' in this case)
>>> if the key is not represented in the query - this is not documented,
>>> but it is commented in the source:
>>>
>>> # @unique_queries = () if there is no 'key' in $input_query
>>>
>>> # Build the final query: Default to the disjunction of the unique
>>> queries,
>>> # but allow the input query in case the ResultSet defines the query
>>> or the
>>> # user is abusing find
>>> my $alias = exists $attrs->{alias} ? $attrs->{alias} : $self- 
>>> >{attrs}
>>> {alias};
>>> my $query = @unique_queries
>>>   ? [ map { $self->_add_alias($_, $alias) } @unique_queries ]
>>>   : $self->_add_alias($input_query, $alias);
>>>
>>> I would say - we should get rid of that 'special feature'.
>>>
>>
>> I would say it's working exactly as intended, you are abusing find  
>> and
>> it's doing the best it can to accomodate you, by creating new objects
>> when your ->find fails to find a matching row.  The only  
>> alternative I
>> can see would be for it to throw an exception when you try and call
>> find_or_create without the
>>
>> --
>> Jason Kohles, RHCA RHCDS RHCE
>> email at jasonkohles.com - http://www.jasonkohles.com/
>> "A witty saying proves nothing."  -- Voltaire
>>
>>
>>
>>
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>>
>
>
>
> -- 
> Zbigniew Lukasiak
> http://brudnopis.blogspot.com/
>
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